1. Field of the Invention
This disclosure relates generally to the field of heat dissipating structures for semiconductor devices, and in particular to a diode laser array assembly.
2. Description of Related Art
High power densities of semiconductor laser radiation are typically needed to optically pump lasers, such as Nd:YAG laser rods. Many configurations of two-dimensional stacked diode lasers are known in the prior art; for example, U.S. Pat. No. 4,716,568 to Scifres et al. describes a stacked array assembly of monolithic laser elements which may be dimensioned to be approximately 1 cm in length, about 0.1 mm thick, and having various cavity lengths. In stacking such laser elements, the arrangement generally determines the overall operation. For example, a stack of laser elements may be oriented about a laser rod such as Nd:YAG to operate in a pulse mode. Alternatively, the stack of laser elements may be configured to operate in a continuous current mode.
However, such arrangements of laser elements, in a package, generate a relatively large amount of heat which is to be dissipated. Such heat is generated by the laser elements due to two factors: electrical series resistance and non-radiative recombination. The series resistance of the total package includes the resistance of the semiconductor material of the laser elements and/or the laser array, as well as the resistances of various metal contacts conveying current to each laser element. The amount of heat generated due to series resistance is generally proportional to I.sup.2 R, in which I is the current flowing through the stacked array, and R is the series resistance of the total package.
In the prior art, heat sinks for such laser elements are known, for example, as described in U.S. Pat. Nos. 5,311,536 to Paoli et al., 5,305,344 to Patel, and 5,040,187 to Karpinski. Microchannel cooling, which is described in U.S. Pat. No. 5,105,429 to Mundigner et al, is another technique in the prior art for extracting the heat generated by the array of laser elements.
Heretofore, such heat dissipative techniques and devices have been somewhat ineffective for high-density packaging of laser elements, such as a plurality of laser diodes closely configured together. A heat dissipative medium or coolant, such as water, is circulated to flow over a set of heat radiating surfaces of a series of laser elements.
In addition, the flow may not allow the coolant to effectively absorb the heat from the most radiative portions of the laser element. For example, in a structure supporting a plurality of laser elements, the path of the flow of water may not be sufficiently close to the most radiative portions of the laser element to absorb the heat therefrom.
A need exists for a stackable laser element, such as a laser bar, and/or a structure mounting such a laser element with improved heat dissipative characteristics.
Typically, the laser elements are configured to be longer in a horizontal direction, and the cooling of such laser elements is performed by passing coolant longitudinally along the horizontal direction along the length of the laser elements. As noted above, the heating of the coolant at one end of the laser element may reduce the efficiency of cooling of the laser elements at another end downstream of the flow. This results in a temperature gradient longitudinally on the laser causing mechanical stressing reducing laser longevity.
Accordingly, a need exists for cooling laser elements which avoids the reduction of efficiency by passing coolant longitudinally in a horizontal direction along the length of the laser elements.
In addition, configurations of stackable laser elements in the prior art have used epoxies and hard soldering to effectively secure the laser elements; for example, to have the laser elements aligned to emit laser radiation in a specific direction. However, in the event that one or more of the laser elements fails or is otherwise defective, the permanence of the laser elements secured together prevents efficient repair and/or replacement of individual laser elements.
Accordingly, a need exists for a stackable laser array element which may be efficiently repaired and/or replaced.
Such laser elements are typically tested prior to assembly in a stack. Accordingly, a need exists for a stackable laser array element which may be effectively tested before stacking.
In addition, laser diode assemblies have typically not employed monitoring devices for ensuring proper operation of the assemblies and the laser elements thereof. Accordingly, the failure of a specific one or a few laser elements has heretofore been difficult to determine for efficient repair and replacement. In addition, such monitoring devices in the prior art may be attached to the outside of the laser diode assembly, which provides relatively inaccurate monitoring since the housing of the assembly prevents positioning of the monitoring devices substantially close to the elements being monitored.
Accordingly, a need exists for a stackable laser array element which permits greater proximity of monitoring devices to the laser elements for improved monitoring and for improved repair and replacement of defective laser elements.